Human Life History

Question 1

Life History is key characteristics that define progress through life (SG)

Answer 1

-Pattern of growth
-Development
-Maturation
-Reproduction
-Mortality

Question 2

Why are life histories important? (SG)

Answer 2

-General trends/patterns
o Limitations, development time, energy requirements
-Human life history affects fitness and disease susceptibility
-Affects reproduction and longevity which in turn affects evolution
-Understanding underpinning mechanisms

Question 3

Understanding 4 underpinning mechanisms for life histories

Answer 3

1. Limitations imposed by mechanical strain on bones – if you are bigger its harder to distribute oxygen and nutrients
2. Energy allocation – more energy b/c bigger brain, fire= more food=bigger brain
3. Longer time required to reach larger size- elephant gestation period 2-3yrs
4. Advantage of a larger body size is traded off against the greater risk of death during a longer maturation period

Question 4

R vs K Reproductive strategies (SG)

Answer 4

R: small, short life span, prey, less intelligent, larger litter, reproduce early, independent early, little care for offspring, small size at birth, high fecundity
K: big, longer lifespan, predator, intelligent, smaller litter, reproduce late, dependent, care for offspring, larger size at birth, low fecundity

Question 5

fecundity

Answer 5

of offspring and individual will have in their whole lifetime

Question 6

Single cycle = semelparous breeding

Answer 6

-Reproduce once before dying
-High investment in mating
-Low investment in individual offspring survival
-Large # of offspring
-Ex: salmon

Question 7

Multiple reproductive events = iteroparous

Answer 7

-High investment in offspring survival
-Long reproductive lifespan
-Trade off = fewer offspring from each mating
-humans

Question 8

Factors affecting Current vs Future reproduction

Answer 8

-Environmental factors affect life history traits – plasticity
-Famine decreases fecundity
o Anorexia and amenorrhea (don’t get period)
-Early puberty and reduced height gain during puberty in cases of famine, childhood abuse…. Etc
o Mechanism enacted to ensure reproduction (evolutionary reason)

Question 9

Extrinsic vs Intrinsic factors of mortality (SG)

Answer 9

-Mortality can be a driver of evolution
-Intrinsic (internal) = physiology like disease
-Humans primarily die from intrinsic factors
-Extrinsic (external)= environmental like prey/predator or accidents
-Increases in extrinsic mortality rates = promotes earlier reproduction and smaller body size
-Smaller body size = smaller offspring = so more vulnerable to prey = so higher # of offspring produced to compensate for high mortality rate

Question 9

Longevity and Body mass (SG)

Answer 9

-Bigger body size = lower extrinsic mortality rates = longer lifespan
-Smaller body size = increased extrinsic mortality rate = shorter lifespan
-Prey = small = high extrinsic mortality = R strategy
-Predator = large = low extrinsic mortality = K strategy

Question 10

Size vs Timing of Sexual Maturity
- 2 competing factors

Answer 10

-Investing energy into continued growth or reproduction?
-2 competing factors:
1. Adult size favors late reproduction where larger female = larger offspring and larger male = more successful mating
2. Mortality risk favors early reproduction

Question 11

Fecundity and Lifespan (SG)

Answer 11

-Increased lifespan → increased body size → lower extrinsic mortality rates → lower # of offspring
-inverse correlation b/w lifespan and # of offspring

Question 12

Longer lifespan and disease

Answer 12

-Natural selection doesn’t operate on disorders that develop after reproduction or if don’t affect reproductive fitness
-Longer lifespan = increased risk for developing late onset disorders (cancer, Alzheimer’s, Parkinson’s….)

Question 13

Mortality risk influences life history

Answer 13

↑ extrinsic mortality → shorter maturity phase → smaller size and shorter lifespan →higher infant mortality (due to small size) → larger # of offspring (to compensate for high infant mortality rates)

Question 14

Human Lifespan

Answer 14

-Low rate of extrinsic mortality factors because we have no predators and cultural & social support
-Extrinsic factors: homicide & accidents
-More energy for growth and learning leads to a prolonged reproductive phase
-Longer lifespan as we have evolved
-Increased incidence of late onset diseases b/c we are living way longer than we used to

Question 15

Body Size (SG)
- is limited by

Answer 15

-Body size is limited by: resources, gravity, cardiovascular system, motility, nutrient availability, … etc.
-Larger you are the longer you survive
-Allometry: body size relationship to different components

Question 16

brain size in humans and life history (SG)

Answer 16

-Increased body weight = increased brain weight
-Humans have 2.5X what is expected for other primates based on our body size
-Brains have high energy consumption: 2% of body weight, 20% of energy consumption, 15% of blood flow
-Larger brains allow for more social and cultural interactions and achievements
-We have immature brains at birth, so they continue to grow post birth
-Larger brain size is associated with social groups

Question 17

How do we develop larger brains? – 2 main ways

Answer 17

1. Grow brains for longer
2. Grow brains faster
   (both ways) Results in: 2x as many neurons that form more synapses to perform its functions

Question 18

Human Life History Stages

Answer 18

-Neonate (birth to 2 months)
-Infancy (2- 36 months)
-Childhood (3-7 years)
-Juvenile (girls = 7-10 and boys = 7-12)
-Puberty and adolescent
-Adulthood (20 to end of childbearing age)
-Senescence (end of childbearing age to death)

Question 19

Human Life history

Answer 19

-Gestation is 280 days
-High parental investment
-Singleton (1 kid at a time)
-1 woman only has a few kids
-Long post-natal dependence
-High survival rate (in prehistoric times only 50% survived)
-Only homos have a childhood phase because it’s for brain growth
-adolescent phase only found in humans because this is where cognitive/ behavioral/social interactions skills develop

Question 20

brain during growth

Answer 20

-at 2 months in utero the brain makes up 50% of its body mass
-adults brain makes of 2% of body mass
-brain metabolism decreases (less energy needed) as brain grows bigger

Question 21

Human infancy stage

Answer 21

-rapid brain and immune development
-goes through many milestones
-after 6 months requires more than breast milk
-maternal milk as primary nutrient source
o stress from limited attachment and sensorimotor experiences
o nutrition required for neural connections
o mother reared vs formula fed chimps have affected growth of white and grey matter in the brain

Question 22

SIDS (SG for factors)

Answer 22

-western cultures at 2-3 months and during sleep
-factors for SIDS: formula fed, low socioeconomic status, premature or low birth weight, smoke exposure, non-back and lone sleeping, over heating soft bedding and materials
-mismatch infant vulnerabilities and dependencies
-campaign say to keep close contact with safe sleeping space

Question 23

Human Childhood

Answer 23

-b/w weening and 7
-constant growth: developing immune system & brain, adrenal androgen production causing mid-growth spurt, permanent teeth
-adult assistance needed: cooperative breeding, social and technical skills learned
-at 7 kids may be able to survive on their own
-unique to the Homo group to give time for brain development

Question 24

stunting (SG)

Answer 24

-sacrificing growth in favor of critical body functions
- long term effects: diminished physical & cognitive development, reduced productive capacity, poor health, increased risk for obesity
- happens early on in growth period and is irreversible
-Recommended actions to help: breastfeeding, scale up prevention, maternal nutrition, community support

Question 25

Juvenile

Answer 25

-7 to puberty (10-14 F & 12-16 M)
-Fully developed immune system
-Not as dependent on parents
-Feed themselves
-Learning social and economic skills

Question 26

(SG) Extension of period between weening and maturity
- bad
- good

Answer 26

-Risky because: predation, nutrient needs, disease, parental support lowers
-But we need it for:
1.Female size requirements (for pregnancy)
2.Social and foraging skills
3.Food competition in larger groups
4.Brain development
5.Immune system development

Question 27

Human Puberty and Adolescence

Answer 27

-Biological maturation: growth acceleration for 2-3 years, derived trait for humans, ends with epiphysial plates closing
-Adolescence is post puberty on the way to adulthood and is unique to humans to give us more time for brain growth and to learn social and communication skills
-Sex differences are in the onset and growth spurt rates where Females are 13-15 and Men 15-17

Question 28

Human Adult

Answer 28

-Completion of brain complexity
-Reproductive life 15-35 years
-Menopause 45-55: oocytes produced in fetal life decline and die

Question 29

Human Fecundity Historical pattern

Answer 29

-Having kids used to be a valuable resource (labor)
-Industrial revolution brought: more food, less work, less disease so higher fecundity rates
-Now having children is a burden and contraception had become available

Question 30

Environment and Reproduction

Answer 30

-Exposure to chemicals in our environment leads to lowering fecundity
-Endocrine disrupting chemicals like BPA can cause: increased risk for obesity/T2DM, decreased fertility & birth weight, increase cancer risk
-BPA: mimics estrogen so disrupts hormonal balance

Question 31

Senescence

Answer 31

-Menopause is not found in other species maybe because no one lives long enough to get to this stage like humans do
-Menopause causes a decline in bone strength
-Female fertility declines before menopause
-Used to have a lifespan of 35-40 but some evidence suggests 60s-70s
-Decline in fertility could be due to a longer lifespan
-Menopause may provide a fitness advantage: grandmother can help rear other kids

Question 32

Death and Birth Pattern with the Industrial Revolution

Answer 32

increased longevity + decreases mortality = bigger population

Question 33

brain growth in humans vs chimps (SG)

Answer 33

Homos have a childhood phase for brains growth and Humans have an adolescence phase to learn social/communication skills while chimps do not have either phase only have infancy, juvenile, and adult phase

Question 34

Why is breastfeeding important to the developing brain? (SG)

Answer 34

b/c breast milk is the primary source of nutrients and is required for the brain to make neural connections and it affects the growth of white/grey matter in the brain
- it can also help prevent SIDS & stunting

Question 35

How has an increased brain size affected life histories? (SG)

Answer 35

increased brain size has helped us make tools, become hunter, master fire, form social bonds and cultural developments to create communities to help us better survive

Question 36

examples of life history affecting disease risk (SG)

Answer 36

• intrinsic mortality- diseases are a main cause
  -Longer lifespan = increased risk for developing late onset disorders (cancer, Alzheimer’s, Parkinson’s….)
• since there is an extension b/w weening and maturity you are more susceptible to disease because immune system not fully formed
• higher fecundity’s during industrial evolution because there was less disease

Question 37

effects of industrial revolution (SG)

Answer 37

• more food, less work, less disease so higher fecundity rates
  -increased longevity + decreases mortality = bigger population